Ultrasound stimulated acoustic emission imaging was recently proposed by Fatemi and Greenleaf for detection of the mechanical frequency response of tissues. This technique exploits interference of two ultrasound beams that have a frequency difference to generate a low frequency vibration in deep focal area. The vibrating tissue acts as an acoustic source with a magnitude that depends of the mechanical response of the tissue. The applicants' hypothesis is that this ultrasound stimulated acoustic emission imaging can be used to monitor and evaluate minimally invasive thermal therapies such as focused ultrasound surgery, RF-ablation, laser surgery, or cryotherapy. The reason for this is that the radiation force (that is responsible for the ability of ultrasound to stimulate the tissue vibrations) is generated by the temperature dependent ultrasonic scattering and absorption in the tissue volume. The initial experiments with ex vivo tissue support this hypothesis. The applicants' plan is: To perform experiments in ex vivo tissue samples to evaluate the temperature dependency of the stimulated acoustic emission signal; To characterize its ability to map tissue coagulation; To detect cavitation both of which could be important for characterizing minimally invasive energy delivery. Finally, they will use the phased array driving hardware and our phased array expertise to demonstrate the potential of utilizing phased arrays for the ultrasound stimulated acoustic emission imaging and test the system for online monitoring of focused ultrasound surgery. The potential benefits of this research are significant. This could make monitoring of minimally invasive thermal an ultrasound therapies much less expensive that the current use of magnetic resonance imaging and could aid in making these methods part of routine clinical practice. In addition, the phased array development will provide an effective method for testing the ultrasound stimulated acoustic imaging in an electronically scanned 2 or 3-D field for diagnostic purposes. Therefore the clinical potential of the proposed research is high with a significant risk of failure due to the preliminary nature of the experimental evidence.